September 2020

Rooflights
Continued from page 36
3Watertightness and water run-off
Another major cause for complaints has
been leaking rooflights causing damage to
roof structures and interior decorations. NARM
has been contacted regarding instances where
the glazing frame has been poorly designed, or
the rooflight has been installed poorly and/or
without sufficient pitch to allow water run-off,
resulting in water building up on the glazing and
eventually penetrating edge seals.
Most high quality glass rooflights incorporate a
glass unit factory bonded into a fully thermally
broken aluminium frame, which includes a drip
detail to ensure the unit is fully watertight as
soon as it is fitted onto an upstand. They should
be sealed to the upstand on site (for airtightness
as well as watertightness), but the seal is only a
secondary seal, rather than the primary means of
preventing water ingress. In some more economic
designs there is no frame, and the glass is simply
sealed to the upstand on site. The absence of any
drip detail on a frame means water can easily
track back on the underside of the glass, and
watertightness of the units becomes entirely
dependent on the quality of the site-applied seal
(often onto an upstand which is not flat and level,
after the upstand itself has been weathered),
which can cause leaks: this style of rooflight
should therefore be avoided.
Glass is not completely rigid and any glass rooflight
will bow slightly under the effect of gravity. Flat
glass rooflights should therefore always be
installed at a slight pitch to avoid ponding (which
would otherwise occur if the bow created a
negative pitch). Typically, smaller rooflights should
be installed at 3 degree pitch, and larger flat glass
rooflights should be installed at 5 degree pitch. You
should always make sure that the contractor who
is building the upstand is aware of this pitch
requirement, to avoid the unsightly problems
associated with ponding (including rapid dirt buildup,
and potentially water ingress).
Some rooflights are offered with “self-cleaning”
glass, which is misleading: true self-cleaning glass
“We’re aware of
rooflights being
supplied for domestic
use with no mention of
Part Q”
(such as Pilkington Activ) works best at pitches
above 30 degrees, with a minimum pitch of 10
degrees so is not suitable for flat glass rooflights.
Some grades of low maintenance or easy clean
glass can be used, but still require regular cleaning.
4Security For domestic properties, Part Q
Building Regulations states that rooflights
deemed as easily accessible need to be
proven to resist criminal attack or incorporate
features that are proven to reduce crime. We’re
aware of rooflights being supplied for domestic
use with no mention of Part Q. Even rooflights
supplied with a laminated inner pane may not
pass Part Q testing as the outer could be broken
and then the inner pane just lifted out of the hole.
5Thermal performance It’s important that
manufacturers state ‘whole product’ U-
values to ensure thermal performance
which will allow compliance with Part L Building
Regulations. Some manufacturers are quoting
‘centre pane’ U-values which do not take into
account edge spacers and frame construction.
The thermal performance of a rooflight must be
considered for the whole assembly, because while
glazing may be compliant, poor frame design can
affect thermal performance. This can result in
higher energy bills for building users and
subsequent unwanted higher CO2 emissions.
Above left & inset: The glazing on this rooflight was not
properly fixed, resulting in it being blown off in windy
weather and ending up in a nearby garden. Luckily, no one
was injured in this instance.
Remember: a great looking rooflight isn’t
necessarily a great rooflight
NARM has noted that in many cases where
complaints have occurred, the manufacturer is
targeting homeowners with sophisticated
websites and literature focusing heavily on the
aesthetics of the product and often claiming
excellence in quality standards. Some have even
referenced NARM documents on their marketing
materials; beware!
In a crowded marketplace, where some
manufacturers are making confusing or untrue
claims, careful consideration needs to be given to
rooflight choice if problems of water ingress,
ponding or worse still, inadequate safety, are to
be avoided.
The good news is that there are many excellent,
trustworthy UK suppliers of properly designed
rooflights which will offer years of safe and
reliable service. One simple and certain way to
ensure you’re dealing with such a company, is to
establish whether your supplier is a NARM
member company. NARM has stringent
membership criteria, a key part of which is that
any product supplied by a member company is
fully compliant with Building Regulations and
meets all required specification and safety
standards.
Contact NARM
www.narm.org.uk
@_NARMUK
38 TC SEPTEMBER 2020